JUNB 4, 1921 DELLINGER AND VVHITTEMORE: RADIO FADING 251 



It has been reported that at sunrise and sunset the shorter waves 

 have the advantage over the longer ones in transmission across the 

 Atlantic. 



At sunrise or sunset at the sending or receiving stations the intensity 

 of signals on long wave-lengths becomes abnormally great. On short 

 wave-lengths, at sunrise at the receiving stations, the signals from 

 distant stations merely become steadier for a moment before they 

 suddenly become inaudible. 



It is possible that the reported differences in the abilities of inland 

 and coastal stations in the United States to receive transatlantic 

 signals may be the result of differences in their relation to the line of 

 sunrise or sunset. 



Effects of time of year. (Intensity and strays.) — Signals from 

 distant stations are much louder on winter nights than on summer 

 nights. Signals become poorer in the spring and it is a question 

 whether this is caused by vegetation, ionization, change in tempera- 

 ture, or other factors. 



Strays are much less frequent and normally much less intense, in 

 winter than in summer. 



Effect of eclipses.— The occurrence of an eclipse has been found 

 to improve signals, even when they pass only through the penumbra. 



Effects of atmospheric electricity, terrestrial magnetism, solar activity. 

 (Intensity.) — In contrast to its effect on wire telegraphy, an aurora 

 has very little effect on radio, except possibly short-wave signals. 

 On an auroral evening none of the usual western stations could be 

 heard at Hartford, Connecticut, but that city did succeed in com- 

 municating with Boston, a thing which, curiously, is usually impossible. 

 On the day after an aurora a Chicago station copied signals from a 

 station in Los Angeles. 



An aurora is preceded by violent variations in the earth's magnetic 

 field, and usually occurs during periods of great sunspot activity. 

 An aurora would seem to be an extreme case of disturbance at or 

 below the Heaviside surface, producing ionization and also strays. 



The conductivity of the atmosphere is somewhat greater at night 

 than during the day. The atmospheric conductivity decreases and 

 the potential gradient increases at the ground level at sunrise and 

 sunset. 



Culver reports that when the potential gradient and the conduc- 

 tivity of the air fluctuate greatly, strays are intense. He reports 

 also that the intensity of strays varies inversely as the solar constant 



